At the priority date of this patent application information transfer between computers over wired or optically coupled networks has become a vital part of everyday life. A vast majority of such information transfer takes place according to or at least takes some partial advantage of various versions of the TCP/IP (Transmission Control Protocol/Internet Protocol), as is illustrated in FIG. 1. In a simple case there are two communicating parties, known as the client 101 and the server 102. The former is the device or arrangement that a user utilizes to download and use information and store it locally, while the latter is a kind of central data storage from which information is to be downloaded. Both the client 101 and the server 102 set up a so-called protocol stack where information is exchanged in the conceptually vertical direction. Layers that are on the same level in the client and the server constitute the so-called peer entities that communicate with each other through all lower layers in the protocol stacks. On top of the pairs of IP layers 103 and TCP layers 104 there may be further higher layers. An example of a protocol layer that is widely used directly above the TCP layer is the HTTP (HyperText Transfer Protocol) that is meant for the transmission of files written in markup languages like HTML (HyperText Markup Language). Other examples of widely used higher protocol layers that in the layer hiearchy are level with HTTP are FTP (File Transfer Protocol), Telnet and SMTP (Simple Mail Transfer Protocol; not shown). The layers that are below the IP layer 103 are not specifically shown in FIG. 1; the person skilled in the art is well aware of those possible lower layers that are used in various communication solutions.
The basic model of two-party communications shown in FIG. 1 contains an inherent assumption that the transmission capacity of all stretches of the communication connection is essentially the same. However, in many real life communication connections there is a certain passage over which only a limited transmission capacity is available. In this patent application we will refer to such a capacity-restricted passage as the limited speed communications link. The transmission capacity that is available for communications over the limited speed communications link determines the overall maximum bit speed that can be obtained in the communication connection between the endpoints of the connection.
Extending the techniques known from wired information transfer into a connection that includes a wireless link, such as a radio connection between a base station and a portable terminal, introduces new aspects that a user is likely to encounter in the form of lower bit rates and increased delays. These are mainly related to two interconnected features of the wireless link in comparison with wired or optically coupled links: inherently lower reliability (i.e. higher susceptibility to transmission errors), which leads to frequent retransmissions, and radio link congestion because a base station can only maintain a limited number of simultaneous connections. These factors together cause the wireless passage often to be the limited speed communications link of a communication connection. In the following we will mainly describe the properties and characteristics of wireless links; the invention has, however, also wider applicability in all kinds of communication connections where a certain passage between two devices limits the overall achievable performance in a connection extending further than just these two devices.
The TCP/IP-based technique of transferring information is not particularly well suited for wireless information transfer. As an example we may consider a typical case of web browsing, where HTTP is used over TCP/IP in a communication connection that goes over a wireless link. Factors that cause the wireless link resources to be wasted to a relatively great extent are:                sending the bulk of the contents from web servers (HTML pages) as plain text;        the multitude of requests: at least in HTTP 1.0 a separate request is issued for every item (e.g. a picture) that exists on a page, so that because TCP in turn establishes a separate connection for every request, there may easily be as many requests as there are items to be downloaded;        the 3-way handshake procedure, i.e. a pair of non-payload messages exchanged between the client and the server, involved in each TCP connection; and        sending the HTML page most often in several packets so that TCP sends an acknowledgement for every one of them.        
A solution that has become reality around the priority date of this patent application is WAP (Wireless Application Protocol). It is a bandwidth-optimized alternative to protocols that are not so optimized, such as the TCP/IP. Optimization involves measures like omitting redundant messages and replacing repeatedly occurring well-known tags with shortened codes. Optimization in this sense aims at the highest possible bandwidth efficiency, which itself has a definition as the ratio of the information transmission rate (the number of information bits transmitted per second) and the bandwidth in Hertz that is allocated for transmitting said information. Bandwidth efficiency measures (not surprisingly) how efficiently the communications system uses the available bandwidth.
The WAP protocol stacks are illustrated in FIG. 2, where the actual WAP layers are, from top to down, the application layer 201 (WAE, Wireless Application Environment), the session layer 202 (WSP, Wireless Session Protocol), the transaction layer 203 (WTP, Wireless Transaction Protocol), the security layer 204 (WTLS, Wireless Transport Layer Security Protocol) and the transport layer 205 (WDP, Wireless Datagram Protocol). In place of the WDP layer an UDP (User Datagram Protocol) layer must be used for IP bearers. Beneath the transport layer 205 there are further lower layers like IP 206 and physical layers 207; together these are also commonly referred to as the bearer layers.
WAP was developed to enable access to networked information from devices that have the typical features of wireless terminals, i.e. limited CPU (Central Processing Unit) capacity, limited memory size, battery-powered operation and simple user interface. The commercial applications of WAP that exist at the priority date of this patent application are the so-called WAP phones that combine the features of a mobile telephone with certain limited functionality of a web browser. In practice we have seen that the small number of WAP users compared to that of wired Internet users is a major drawback that reduces the commercial interest in setting up WAP services, especially at the advent of third generation digital cellular networks. Moreover, already due to the introduction of the first phase of packet-switched cellular data networks using GPRS (General Packet Radio Service) the need of wireless access for full-fledged mobile clients is expected to grow considerably. WAP is not suitable for providing that, so there have been devised various proprietary solutions for wireless data transfer.
As an example of the last-mentioned FIG. 3 illustrates the so-called MOWGLI concept (Mobile Office Workstations using GSM Links) where a mobile workstation 301 utilises a wireless link between a GSM (Global System for Mobile telecommunications) cellular phone 302 and a GSM base station 303 to communicate with what is called a mobile-connection host 304. In the mobile workstation 301 old applications 311 and 312 communicate with agent programs 313, 314 and 315 through an application programming interface known as the Mowgli Socket API 316. From the agents there is a connection to a Mowgli Data Channel Service API 317 and the associated Mowgli Data Channel Service 318 either directly or through a Mowgli Data Transfer Service API 319 and the associated Mowgli Data Transfer Service 320. New mobile applications 321 may have been designed to communicate directly (through the appropriate API) with either the Mowgli Data Transfer Service 320 or the Mowgli Data Channel Service 318. A control tool 322 is included for controlling the operation of the other program components. A wireless interface block 323 constitutes the connection from the mobile workstation 301 to the cellular phone 302.
In the mobile-connection host 304 there are counterparts for certain entities implemented in the mobile workstation 301: a wireless interface block 331, a Mowgli Data Channel Service 332 with its associated API 333 as well as a Mowgli Data Transfer Service 334 with its associated API 335. A number of proxies 336, 337, 338 and 339 may act in the mobile-connection host 304 as counterparts to the agent programs 313, 314 and 315 in the mobile workstation 301. An arrangement of a socket API 341, a TCP/UDP layer 342 and an IP or mobile IP layer 343 constitute, together with a network interface 344, a connection from the mobile-connection host 304 further to a LAN 345 or a similar network. Under the IP or mobile IP layer 343 there may also be a virtual network interface 346.
The division of the MOWGLI architecture into Agent/Proxy-, Data Transfer- and Data Transport layers is shown with heavy dotted lines in FIG. 3. Of the protocols used therein, between an agent and a proxy (like the master agent 314 at the mobile workstation 301 and the master proxy 338 at the mobile-connection host 304) there is a Mowgli Socket protocol, between the mutually corresponding MDTS entities 320 and 334 there is a Mowgli Data Transfer protocol and between the mutually corresponding MDCS entities 318 and 332 there is a Mowgli Data Channel protocol.